Water-insolubilized polymers of specific (meth)acrylamide derivatives absorb water in aqueous solutions to form hydrated gels. The hydrated gels have a temperature-dependent nature according to which the amount of water absorbed therein varies with temperature. Making use of this characteristic, it has been desired to develop their applications in various field. Further, it is known that water-insolubilized polymers of the (meth)acrylamide derivatives are inherently rendered hydrophobic by heating and hydrophilic by cooling in aqueous solutions, that is, they have a characteristic of varying their nature from hydrophobic to hydrophilic or vice versa with temperature. As a result, their application to separation functional materials has also been investigated, for instance, as in U.S. Pat. Nos. 4,729,834, 4,683,258 and 4,828,710, which are the patent applications of the present inventors.
In all of these cases, however, it is necessary to form the materials into shapes in accordance with their uses, and in the application to separation functional materials in particular, preparation of granular polymers is indispensable.
As conventional processes for preparing granular polymers, there are the suspension polymerization process using water as the continuous phase for hydrophobic polymers and the so-called reverse phase suspension polymerization process using oil as the continuous phase for hydrophilic polymers.
(Meth)acrylamide derivatives generally combine both hydrophobic and hydrophilic properties to a more or lesser extent. Accordingly, the application of conventional techniques as is may often lead to failure in the production of granular polymers by the foregoing processes.
For example, in the suspension polymerization using water as the continuous phase, (meth)acrylamide derivatives are often soluble in water. In such cases, it has been attempted to reduce their solubilities through salting-out effects by the addition of water-soluble inorganic salts. In such case, however, it has been necessary to add various additives, for instance, polymer stabilizers such as sodium polyacrylate and carboxymethyl cellulose and, in some cases, surface active agents such as sodium dodecylbenzenesulfonate to the aqueous solutions in which the inorganic salts are dissolved at high concentrations, as shown in Kobunshi Ronbun-shu (High Polymer Report) Vol. 40 No. 7, p441-447 (1983).
Therefore, in the production of granular polymers according to the foregoing processes, it has been unavoidable to involve difficult and troublesome operations, such as, stable dissolution or dispersion of the above various additives prior to polymerization, stable maintenance of the dispersed state during polymerization, washing-out of the above additives from the granular polymers after polymerization, etc. These operations raise serious problems in the production of granular polymers
The present inventors have discovered that granular polymers can be prepared favorably even in the absence of the foregoing additives by polymerizing the derivatives in aqueous inorganic salt solutions in which inorganic particulates are suspended.